This research is designed to contribute to a comparative study of the regulation of seizing-and-biting in vertebrates during states of central nervous system arousal leading to predatory attack and related events. It is a basic inquiry into the interplay of peripheral and central nervous system participation in the formulation, timing and regulation of adaptive behavior patterns. The brain physiology of the shark is practically unexplored. But the shark is in many ways a most suitable animal for the proposed study. (1) It is very close to the evolutionary origins of the jaw armature and its attendant nervous mechanisms directing predation. It is reasonable to suppose that more recently evolved vertebrates have added on to basic mechanisms found in the predatory elasmo-branch in the development of certain kinds of behavior. (2) The shark's gross cerebral anatomy provides easy access to certain cell groups which are rather difficult to reach effectively in advanced vertebrates for physiological investigation. Guided by knowledge of the control of predatory mechanisms in the cat, a search will be made for similar mechanisms in the immobilized shark. As a beginning, intracellular recordings of synaptic and spike potentials from cells of the trigeminal motor and mesencephalic nuclei will be used as indices of facilitation produced at these stations in the integration of jaw action by central sources of nervous activity, peripheral sources and combinations of these. Stimulation of the nervous system will be by electrical means, or by adequate sensory means where appropriate. Based on old and new anatomical evidence, a new role for the mesencephalic nucleus is suggested and will be tested.